Hard Boiled Egg
Something nice and easy for the weekend….
You are the worlds finest chef, currently working at the finest restaurant in Puzzlaria.
One December morning after a particularly heavy snow storm, the power fails. Fortunately, there is still an old wood stove with which you can prepare most of the meals. However one cantankerous customer, Zaux, has a peculiar item which now poses a problem. He likes a single egg boiled for exactly nine minutes.
You aren’t wearing your watch, and all the clocks in the building are electric. You are able to find two exquisite hourglasses, able to pricely measure in (hand-crafted swiss) sand seven and four minutes, respectively.
How quickly using only these two hourglasses can you provide Zaux with his egg?